1. Field of the Invention
The present invention relates to a charging member preferably used as a charging device, etc., mounted on an electrophotographic apparatus. In particular, the present invention relates to a charging member preferably used as, for example, a transfer roller for charging transfer materials and a charging roller for charging photosensitive members.
2. Description of the Related Art
Charging members such as transfer rollers for charging transfer materials and charging rollers for charging photosensitive members are mounted on electrophotographic apparatuses such as copying machines and optical printers.
For example, when a toner image developed and formed on an image-holding member, e.g., a photosensitive member, an intermediate transfer member, a transfer drum, is transferred on a transfer material, e.g., paper, the transfer material is press-contacted to the image-holding member using the transfer roller, and at the same time, the transfer material is electrified by being supplied a charge with the polarity opposite to that of a toner so that the toner is adsorbed on the transfer material and the toner image is transferred.
Herein, the density of the charge being supplied to the transfer material affects the quality of the resulting image to a great degree. That is, when the charge density is insufficient, since the force for adsorbing the toner is decreased, particularly in the case in which the transfer material is a dry paper, a problem of so-called xe2x80x9csplashingxe2x80x9d may be occurred. On the other hand, when the charge density is in an excessive degree, the blurring may be occurred due to the toner being electrified to have the opposite polarity so that a high quality of image may not be produced. Therefore, in order to realize good control of the charge density, a charging material used as the transfer roller, etc., is required, for example, to have an electrical resistance with ease in control, and furthermore, with no large fluctuation for a long time.
In addition, the uniformity of the charge density affects the quality of the resulting image to a great degree. That is, when the charge density is not uniform, unevenness in concentration in transfer of a solid black image and fleck-like unevenness so-called xe2x80x9csand-like areaxe2x80x9d in the transferred image may be occurred. Therefore, in order to realize high uniformity in the charge density, the charging member used as the transfer roller, etc., is required, for example, to have small variations in electrical resistances according to positions.
As another example of the charging member, the charging roller can be mentioned. That is, in the electrophotographic apparatus, in order to suppress unevenness in the image concentration, and to suppress separation and retransfer, the photosensitive member is required to be uniformly electrified before an electrical latent image is formed on the photosensitive member. Hitherto, a corona charging device has been used for charging the photosensitive member. In the case in which the corona charging device is used, there have been, however, problems in that ozone is generated, a pinhole may be generated in the surface layer of the photosensitive member due to an abnormal discharge, etc. On the other hand, in the case in which the charging roller is used for charging the photosensitive member, since no discharge is occurred, and the charging is performed while the charging roller, the predetermined voltage being applied thereto, is closed to or contacted with the photosensitive member, the aforementioned problems are suppressed.
The charging member used as the aforementioned charging roller, etc., may be filled with, for example, carbon black, graphite, metallic oxides such as titanium oxide and tin oxide, metallic powders such as copper and silver, and particles with conductive coatings, so that the electrical resistance is controlled to be a predetermined value. In order to suppress unevenness in electrification, destruction of the photosensitive member due to a partial leakage, etc., it is required that the electrical resistance of used charging member is controlled with ease and local variations in electrical resistances are suppressed.
In order to realize the aforementioned properties required of the charging member, various suggestions have been made until now.
For example, it is disclosed in Japanese Patent Laid-Open No. 8-159148 that the variations in volume resistivity of the roll are suppressed by the rubber roll including the first layer made of a polar rubber and the second layer made of a synthetic resin covering around the perimeter of the first layer so as to realize uniformity in the image property. Even when the resin layer is formed on the polar rubber layer as disclosed in the aforementioned specifications, it is, however, believed that the effect of the second layer made of the synthetic resin being provided may be insufficient as long as the volume resistivity of the polar rubber layer itself is not improved in uniformity and durability.
It is disclosed in Japanese Patent Laid-Open No. 10-87897 that the hardness and the electrical resistance are controlled in the predetermined range so as to realize uniformity in the conductivity by a rubber composition containing the vulcanized product of the rubber component A, the rubber component B vulcanized in a mechanism different from that in the rubber component A, the conductive particle, and at least one antioxidant selected from the group consisting of hydroquinone derivatives and phenol derivatives. In the aforementioned specifications, it is described that desired electrical resistance and uniformity in the conductivity are realized by the addition of the predetermined antioxidant, it is, however, not described in details regarding the promotion of the vulcanization reaction, etc.
It is described in Japanese Patent Laid-Open No. 9-34215 that diazabicycloamine is used in the manufacture of the charging member using a urethane rubber. Since diazabicycloamine, however, abruptly reacts with urethane as temperature is elevated, unevenness in the cross-linking reaction is likely to be occurred. Therefore, particularly in the case in which molding is performed in a mold, unevenness in the cross-link is occurred due to temperature variations in the mold so that there are problems in that unevenness in the hardness and unevenness in the resistance in the molded material are likely to be occurred.
In consideration of the aforementioned circumstances, objects of the present invention are to provide a charging member in which the electrical resistance is controlled with ease, the electrical resistance is uniform, and the electrical resistance, chemical properties, mechanical properties, etc., are suppressed to vary with time so as to exhibit excellent durability, and to further provide an electrophotographic apparatus exhibiting superior performances provided with a charging device produced using the aforementioned charging member.
The present invention was made to achieve the aforementioned objects. According to the present invention, a charging member primarily containing 100 parts by weight of at least one kind of polar rubber including at least a nitrile rubber, further containing at least 0.01 parts by weight or more and 5 parts by weight or less of diazabicycloamine compound and 0.01 parts by weight or more and 10 parts by weight or less of weakly acidic compound is provided. That is, according to the present invention, the charging member having superior properties in, for example, permanent compression set and abrasion resistance by the nitrile rubber being vulcanized using diazabicycloamine as a vulcanization accelerator.
Furthermore, the resistance can be controlled with ease according to the additive amount thereof, and the charging member in which the resistance variations due to humidity are also suppressed can be produced.
A hydrin rubber has good reactivity similar to that of the nitrile rubber and has effects not only on the permanent compression set, but also on the resistance variations due to endurance. In the case in which those are used as a mixture, co-vulcanization proceeds in spite of difference in reactivity between those so that the charging member having combined superior properties with no degradation in each property can be produced.
The reasons such a superior charging member can be produced are believed that the diazabicycloamine compound has a function of accelerating vulcanization not abruptly being increased with elevation in temperature, and furthermore, the nitrile rubber and the diazabicycloamine compound are superior in dispersiveness and reactivity therebetween.